Electrical open/short contact alignment structure for active region vs. gate region

ABSTRACT

A method is disclosed for measuring alignment of polysilicon shapes relative to a silicon area wherein the presence of an electrical coupling is used to determine the presence of bias or misalignment. Bridging vertices on the polysilicon shapes are formed. Bridging vertices over the silicon area create low resistance connections between those bridging vertices and the silicon area; other bridging vertices over ROX (recessed oxide) areas do not create low resistance connections between those other bridging vertices and the silicon area. Determining which bridging vertices have low resistance connections to the silicon area and how many bridging vertices have low resistance connections to the silicon area are used to determine the bias and misalignment of the polysilicon shapes relative to the silicon area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of a patent application of thesame title, Ser. No. 10/944,625 filed on Sep. 17, 2004, now Pat. No.7,183,780 issued on Feb. 27, 2007, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The current invention generally relates to integrated circuit design andfabrication. More specifically, the current invention relates tosilicide semiconductor production processes.

2. Description of the Related Art

Continuous improvements in the design and fabrication of microelectronicdevices have led to smaller and faster computing devices capable ofsolving increasingly complex problems. Rapid gains in the performance ofthese devices have enabled technology users to solve increasinglycomplex problems. However, increasingly complex problems have demandedlarger amounts of computing power, and as a result, more microelectronicdevices such as field effect transistors (FETs) are needed to performthe necessary computations. Moreover, while the demand for computingpower has increased the transistor counts on computer chips, physicalchip size has been reduced or held constant thus complicating design andfabrication processes.

Semiconductor chips are composed of several basic elements: a collectionof active components such as FETs, signal conductors such as metal orsuitably doped polysilicon that transmit electrical signals betweenthese components, and insulating (or “dielectric”) material thatseparates the metal traces from one another. To produce consistentbatches of computer chips, a formal production process is employedcontaining four high-level steps: microlithography, implantation,deposition and etching. Modern computer chips currently contain millionsof transistors that are printed during the microlithography stage usinga light source that ranges in wavelength from 130 to 90 nanometers. Eachtransistor is then implanted with, e.g., boron or phosphorous toeffectively dope the transistor creating a device capable of behaving asa conductor or an insulator based on its electrical properties and thevoltage applied. The ability to switch between a conductor and aninsulator facilitates the binary behavior necessary for moderncomputing. Reducing the size of the field effect transistor lowers thevoltage necessary to switch between a conductor and an insulator.Furthermore, smaller FETs that require less voltage also require lesstime to switch. Thus, it is desirable to create smaller FETs because ofthe performance gains and cost savings resulting from smaller featuresizes.

The production methods used to fabricate field effect transistors arewell known in the art of manufacturing microelectronic devices. Themethods known are expensive processes that require a significant numberof steps and generally require over a month to complete. In a massproduction environment, eliminating one or more steps can result inexpense savings and increased profits for both the manufacturer and theconsumer. As a result, large amounts of research and development aredirected at eliminating steps of the fabrication process and improvingthe design of FETs.

Referring to FIG. 1, a silicon on insulator FET is comprised of apolysilicon shape 8 positioned on a silicon substrate patterned withoxide areas and doped silicon areas. Portions of the silicon have beendoped and comprise a source 5 and a drain 6 of the FET, which areindividually positioned on either side of the polysilicon shape 8. Theelectrical signal generated by the switching of the FET is transmittedthrough separate couplings created on both the source 5 and the drain 6.These couplings historically use vias, which are holes formed in thelayers of the chip. The vias are filled with a conductive material suchas tungsten, aluminum, or copper permitting the signals to becommunicated from the source 5 or drain 6 of the FET to othermicroelectronic devices using signal conductors such as metalspreviously mentioned. FETs are produced using a self-aligned process toblock implants into source and drain regions of a silicon area.

One step in the process of making FETs involves aligning the polysiliconwith the silicon area to ensure that the FETs operate according topreset specifications. The alignment process is never perfect; however,the overlay alignment measurement is critical for FET operation and mustbe tightly and measurably controlled during manufacture. Currently,there is no accurate measurement of this important parameter that can bedone effectively and at low cost. U.S. Pat. No. 5,699,282 uses atechnique of alignment measurement that performs electricalmeasurements. The technique employed requires vias and metalinterconnections. Vias and metal interconnections consume valuabledesign space, which could be used more efficiently for chip testfunction. Metal interconnection uses up valuable space that is needed tointerconnect logical blocks on the semiconductor chip. Therefore, a needexists to create an accurate process that properly measures alignmenterrors that occur during the manufacture of the semiconductor chip.

Modern semiconductor processes include a silicide step, in which asuitable metal, such as titanium, is deposited on the chip and the chipis heated forming silicide on the sources, drains, and polysilicon whichprovides those areas with a lower electrical resistance. An example ofthis prior art design is illustrated in FIG. 1 where source 5 has asource silicide portion 10, drain 6 has a drain silicide portion 13, andpolysilicon shape 8 has a polysilicon shape silicide portion 12.

Another particular step in the process of creating FETs involves thecreation of a spacer 9A, 9B, which ensures separation of silicideportions of the polysilicon shape 8 from the silicon areas (source 5 anddrain 6) to prevent electrical silicide bridging (shorts) between thepolysilicon shape 8 and the source 5 and drain 6. The spacer 9A, 9B isgenerally a silicon oxide composition or other dielectric material. InU.S. Pat. No. 4,983,544, a method is proposed to facilitate theformation of an electrical bridge using silicide as a bridge contactrather than a via or other metal interconnect. It is advantageous tohave different interconnection alternatives that give circuit designersadditional flexibility when designing circuit layouts. However, U.S.Pat. No. 4,983,544 achieves this flexibility only by providing a maskand subsequent etching steps for selectively etching portions ofspacers, thereby exposing corresponding vertical surfaces of polysiliconshapes to a subsequent silicide process, forming an electricallyconducting silicide bridge between the polysilicon shape and the siliconarea. Controlling precision in the etching process is a difficult task,and also requires that an additional etching step be inserted into thetransistor fabrication process requiring more time and additionaletching materials expenses.

Also, it is presently not desirable and considered a groundrule designviolation to form a polysilicon shape containing a small angle such thatwhen a spacer is formed on a polysilicon shape, a portion of a verticalsurface of the polysilicon shape becomes silicided and can becomeshorted to the silicon area. If such a design were permitted to exist inthe current state of the art, FET designs would not function as designeddue to shorts that would occur between the exposed polysilicon and thesilicon area.

It would be advantageous to have an alternative method to thetraditional via coupling that facilitates the interconnection ofmicroelectronic devices while simultaneously reducing circuit layoutconstraints and fabrication requirements. Therefore, a need exists tocreate an alternative method to interconnect microelectronic devicesthat does not require a via coupling between the metal layer and siliconareas. Furthermore, it is desirable to compact more microelectronicdevices into a smaller area. A need also exists to decrease the amountof space required to accommodate a specified number of microelectronicdevices and the accompanying metal interconnects. Simplified contactstructures, which require less space will result in higher chipdensities, lower production costs, increased performance, and reducedpower consumption.

SUMMARY OF THE INVENTION

The present invention provides a method of forming an electricalcoupling between a polysilicon shape and a silicon area on asemiconductor chip. One embodiment of this method is forming apolysilicon shape having a bridging vertex over a silicon area, creatinga spacer on a vertical side of the polysilicon shape except on thebridging vertex, and applying a silicide to the polysilicon shape and tothe silicon area thereby creating an electrical coupling between thepolysilicon shape and the silicon area at the bridging vertex.Advantageously, no separate mask and special etching step to removeportions of the process are required.

Another aspect of the present invention is a semiconductor device thatcomprises a polysilicon shape having a bridging vertex formed over asilicon area, a spacer on a vertical side of the polysilicon shapeexcept on the bridging vertex, and a silicide formed on the polysiliconshape and on the silicon area thereby creating an electrical couplingbetween the polysilicon shape and the silicon area at the bridgingvertex.

Yet another aspect of the present invention is a circuit comprising oneor more semiconductor devices that each comprises a polysilicon shapehaving a bridging vertex, the bridging vertex formed over a siliconarea, a spacer on a vertical side of the polysilicon shape except on thebridging vertex, and a silicide formed on the polysilicon shape and onthe silicon area thereby creating an electrical coupling between thepolysilicon shape and the silicon area at the bridging vertex.

Another aspect of the present invention is a method of measuringalignment and bias of a polysilicon shape to a silicon area. Oneembodiment of this method comprises forming a polysilicon shape to havea bridging vertex, the bridging vertex formed near a silicon area anddetermining if an electrical bridge exists between the polysilicon shapeat the bridging vertex and the silicon area.

Another aspect of the present invention is an apparatus for measuringalignment and bias between a polysilicon shape and a silicon area. Oneembodiment of this apparatus comprises a silicon area, a plurality ofbridging vertices positioned near the active area, wherein each bridgingvertex of the plurality of bridging vertices is uniquely positionedrelative to the silicon area, and wherein each bridging vertex of theplurality of bridging vertices is coupled to an electrical source.

The present invention offers numerous advantages over conventionalsemiconductor schemes. For example, embodiments of the present inventionrequire less design space and provide design engineers with alternativemethods of interconnection for microelectronic devices. Embodiments ofthe present invention can also be used to more efficiently measurealignment and bias present in a microelectronic device. These and otherfeatures, aspects, and advantages will become better understood withreference to the following description, appended claims, andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art drawing illustrating a simplified isometric viewof a conventional silicon on insulator (SOI) field effect transistor(FET).

FIG. 2 is a prior art cross-sectional drawing further illustrating thedesign of a conventional silicon on insulator field effect transistor.

FIG. 3A-3F are top views of a polysilicon shape and spacers formed onboth sides of the polysilicon shape. FIG. 3C-3F further illustratespacer behavior around bridging vertices and critical angles.

FIG. 3H is an isometric drawing of a spacer, bridging vertex, andpolysilicon shape demonstrating thinning of the spacer near the bridgingvertex.

FIG. 4 is a simplified, cross-sectional view of a semiconductor andillustrates a silicide bridge.

FIG. 5 is a top view diagram illustrating multiple bridging verticescoupling a polysilicon shape to a silicon area.

FIG. 6 is a top-view illustration of a circuit implementing multipleFETs containing bridging vertices.

FIG. 7 is an isometric prior art drawing of a FinFET.

FIG. 8 is a prior art top-view illustration of a via interconnect notutilizing bridging vertices.

FIG. 9 is a top-view illustration of a functionally equivalentembodiment to the illustration shown in FIG. 8, but utilizing bridgingvertices in place of a via.

FIG. 10A is a top-view illustration of a measuring apparatus having aplurality of polysilicon shape pairs and a silicon area.

FIG. 10B is a top-view illustration similar to FIG. 10A, but having asilicon area exhibiting bias.

FIG. 11 is a table illustrating example bias and misalignmentmeasurement results.

FIGS. 12A, 12B, and 12C are top view illustrations of a measuringapparatus comprises of polysilicon shape pairs and a silicon area.

FIGS. 13A and 13B is a flow chart describing a method for measuring biasand misalignment of polysilicon shapes relative to a silicon area.

FIG. 14 is a flow chart describing a method for forming a field effecttransistor (FET) containing a bridging vertex and resulting electricalcoupling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described in detail with reference to the figures.It will be appreciated that this description and these figures are forillustrative purposes only, and are not intended to limit the scope ofthe invention. In particular, various descriptions and illustrations ofthe applicability, use, and advantages of the invention are exemplaryonly, and do not define the scope of the invention. Accordingly, allquestions of scope must be resolved only from claims set forth elsewherein this disclosure.

The current invention teaches methods and apparatus to create asemiconductor device having a bridging vertex formed on a polysiliconshape to create an electrically conducting bridge between thepolysilicon shape and a silicon area at the bridging vertex.

FIG. 1 is a prior art drawing illustrating a simplified isometric viewof a conventional silicon on insulator (SOI) field effect transistor(FET). Although a SOI process is used for illustration, the invention isnot limited to SOI processes. In an SOI FET production process, a buriedoxide (BOX) 2 is first formed in a silicon substrate 3. Generally,silicon substrate 3 is lightly doped, and a P− substrate is commonlyused. After buried oxide 2 has formed, another layer of siliconsubstrate 3 or suitably doped silicon such as silicon germanium isformed on the buried oxide 2. Alternatively, if buried oxide 2 is formedby oxygen implant, a portion of silicon substrate 3 remains above buriedoxide 2, and can be used to make FET devices. Following the creation ofburied oxide 2, recessed oxide (ROX) areas are formed (not shown) asareas where no semiconductor devices will be formed. A thin oxide layer4 is then created followed by the formation of a polysilicon shape 8.Thin oxide layer 4 is then etched away except for areas on whichpolysilicon shape 8 has been formed. Portions of silicon substrate 3 arethen generally implanted with ions to create a source 5 and a drain 6.In a conventional PFET, body 7 will be doped N−. Conversely, in aconventional NFET, body 7 will be doped P−. Areas not in ROX areas aresilicon areas, including in FIG. 1, source 5, drain 6, and body 7.Spacers 9A, 9B are then created on the vertical sides of polysiliconshape 8. Following this step, a suicide step creates suicide on exposedsurfaces of source 5, drain 6, and polysilicon shape 8 by coating thechip with titanium or other suitable material and heating the structureto create source silicide 10, drain silicide 13, and polysilicon shapesilicide 12. The silicide will be created only on exposed silicon orpolysilicon surface areas that have not been covered by an insulatingcomposition such as a spacer (i.e. oxide). The application of silicideto select areas of the semiconductor increases conductivity.

FIG. 2 is a prior art drawing further illustrating the design of aconventional silicon on insulator (SOI) field effect transistor (FET).In FIG. 2, an insulating layer of dielectric 17 is shown. Dielectric 17creates an insulating barrier between metal layer 15A, 15B and source 5and drain 6. Metal layer 15A and 15B are used to transfer electricalsignals between two or more semiconductor devices and use vias 16A, 16Bas means to transfer electrical signals from source 5 and drain 6 tometal layer 15A, 15B. Vias 16A, 16B are physical holes created indielectric 17 using methods such as drilling, etching, or chemicalbathing and require the use of a mask. The physical holes are filledwith electrically conductive materials such as titanium, aluminum,copper, or tungsten permitting the transfer of electrical signals.

FIG. 3A is a top view of a polysilicon shape 31 and spacers 30A, 30Bformed on both sides of polysilicon shape 31. The spacers 30A, 30Bprevent silicide from forming on vertical surfaces of polysilicon shape31, which could result in electrical bridging between silicide formed onpolysilicon shape 31 and silicide formed on a silicon area 37. Spacerswill be referred to generically as spacer 30, with a letter appended toidentify a particular spacer in a figure. FIG. 3A illustrates aconsistent spacer width along the length of polysilicon shape 31 thatremains straight in its entirety. FIG. 3B illustrates a thinning ofspacer 30A and 30B on angles less than 180 degrees, and a thickeningbehavior of spacer 30A and 30B when applied to polysilicon shape 31containing an angle greater than 180 degrees. In the case of FIG. 3B,the width of spacer 30A has increased where a first polysilicon angle32, 32′ is greater than 180 degrees when the angle measurement is takenon the inner region of polysilicon shape 31 as shown by the curved linehaving two arrowheads. A second polysilicon shape angle 33,33′illustrates spacer thinning that accompanies a polysilicon shape angle33, 33′ of less than 180 degrees when the measurement is taken on theinner surface of the polysilicon shape 31.

FIG. 3C illustrates a bridging vertex 34 (circled), which is createdwhen polysilicon shape 31 is formed having angle equal to or less than acritical angle 35. Bridging vertex 34 is a portion of a polysiliconshape 31 positioned near silicon area 37 such that an electrical bridgeexists between silicon area 37 and polysilicon shape 31. The meaning of“near” when used to define a bridging vertex is further defined as aproximate distance between a bridging vertex and a silicon area whichcreates an electrical coupling between the bridging vertex and thesilicon area. If a polysilicon shape is formed with a bridging vertexpositioned over a silicon area, an electrical connection (a lowresistance connection or short) will be formed between the bridgingvertex and the silicon area. If a polysilicon shape is formed with abridging vertex formed over a ROX area, a low resistance connection isnot made to any silicon area.

In embodiment 3C, a vertical surface of polysilicon shape 31 is notcovered by spacer 30E or 30F and is therefore exposed to the silicideprocess. Silicide forms on the vertical surface of polysilicon shape 31at the bridging vertex 34, and creates an electrical bridge to siliconarea 37. The design of this embodiment is advantageous because bridgingvertex 34 eliminates the need to create a via, requires less space thana via, and reduces the amount of metal required for an interconnectionin a design; thus, couplings to transmit electrical signals can beimplemented between polysilicon shape 31 and silicon area 37 without avia, without a special mask to selectively etch portions of spacers, andwithout a separate step to remove a portion of a spacer. A criticalaspect of this design is the formation of polysilicon shape 31 having abridging vertex defined by an angle less than or equal to critical angle35. Critical angle 35 is the angle at which the spacer width becomessufficiently small to create an electrical bridge between polysiliconshape 31 and silicon area 37. Silicide formed on the exposed verticalwall of polysilicon shape 31 results in the formation of a silicidebridge over a thin oxide (similar to thin oxide 4 in FIG. 1), shortingpolysilicon shape 31 to silicon area 37. Critical angle 35 required tocreate a bridging vertex depends on the materials used to create spacerwidth of spacer 30, thickness of the thin oxide, production processesused to create the FET, and the precision of the process used tomanufacture the FET.

FIG. 3D, 3E, 3F are additional exemplary embodiments containingpolysilicon shape 31 that result in bridging vertex 34. Bridgingvertices in FIGS. 3E and 3F use slightly curved surfaces in place ofpointed designs as illustrated in FIGS. 3C and 3D. Therefore, asillustrated in FIG. 3C, 3D, 3E, 3F the construction of bridging vertex34 requires only a polysilicon shape that causes an electricallyconducting silicide bridge be formed. FIG. 3C-3F illustrates variationsof bridging vertex 34; however, innumerable variations exists and allsuch variations achieving a bridging vertex 34 are contemplated andwithin the scope of this invention. FIG. 3H is an isometric illustrationof polysilicon shape 31 containing bridging vertex 34. In thisillustration, spacer 30 thins and thus exposes polysilicon shape 31 tothe silicide process on a vertical side 39; the silicide formed onvertical side 39 forming a silicide bridge to silicon area 37, whichcreates an electrical bridge. Note that in FIG. 3H, for simplicity,spacer 30 is illustrated on only one side of polysilicon shape 31;however, in an actual embodiment both vertical sides of polysiliconshape 31 will have spacers 30.

FIG. 4 illustrates a silicide bridge 40 that exists between a siliconarea 46 and a polysilicon shape 43. Before silicide is applied topolysilicon shape 43 or silicon area 46, no electrical bridging occursbetween the two regions because a thin oxide layer 48 insulates the tworegions. To illustrate an electrical bridge created from silicide, asilicide bridge 40 is illustrated that electrically couples polysiliconshape 43 and silicon area 46. When the width a spacer 30 becomessufficiently small, a portion of one or more vertical sides ofpolysilicon shape 43 are left exposed to a subsequent silicideprocessing step. In the subsequent suicide processing step, suicide iscreated on areas of polysilicon shape 43 that were left exposed, andsuicide bridge 40 is formed between polysilicon shape suicide 42 andsilicon area silicide 45. Note in particular that in absence of aspacer, silicide forms on vertical surface 44 of polysilicon shape 43.Also, polysilicon shape silicide 42 is electrically coupled topolysilicon shape 43 and also that silicon area silicide 45 iselectrically coupled to silicon area 46. It is relevant to note herethat the thickness of thin oxide 48 is extremely thin and is on theorder of 10 angstroms today. Three silicide regions are created duringthe silicide process: polysilicon shape silicide 42, silicide bridge 40,and silicon area silicide 45. Note the lines that exist in FIG. 4 todistinguish the silicide regions are exemplary only and do not exist inan actual embodiment; therefore, the silicide regions should be viewedas one continuous region.

FIG. 5 is an exemplary top view of an embodiment containing multiplebridging vertices 34. Bridging vertices 34, as described above, providesan electrical short between polysilicon shape 31 and a silicon area 56.Surrounding polysilicon shape 31 is a spacer 51 that prevents electricalbridging from occurring between polysilicon shape 31 and silicon area 56except at the bridging vertices 34. The area of polysilicon shape 31that is covered by spacer 51 will be defined as an insulated region 52.Furthermore, insulated region 52 is defined as any part of polysiliconshape 31 that is not coupled to silicon area 56 by way of a silicidebridge 40 (FIG. 4). Another bridging vertex 55 is illustrated as an areaof polysilicon shape 31 where a vertical surface of polysilicon shape 31was exposed to silicide, but is not electrically coupled to silicon area56. In FIG. 5, bridging vertex 55 is positioned over a ROX region 57where no electrical coupling can occur, and thus while bridging vertex55 is silicided on vertical surfaces, it does not electrically short toany other conductor.

FIG. 6 is an exemplary embodiment of an inverter circuit 60 comprisingNFET 61 and PFET 62 employing multiple bridging vertices 34 (allcircled). Note that bridging vertex 34 pertains to a generic bridgingvertex, while particular instances of a bridging vertex are denoted byappending a letter, e.g. 34A, 34B. For simplicity, spacers are notdrawn, but as taught earlier exist on the vertical walls of thepolysilicon shapes and are not present at the bridging vertices. Apolysilicon shape 31A is the gate of NFET 61 and PFET 62. A polysiliconshape 31B is shown containing bridging vertices 34A. In this embodiment,the polysilicon shape 31B is routed over NFET silicon area 63 and PFETsilicon area 64 coupling an NFET drain 65 to a PFET drain 66. Bridgingvertices 34B are formed to connect an NFET source 67A to a groundpolysilicon shape 68. Bridging vertices 34C are used to connect PFETsource 67B to VDD polysilicon shape 69.

FIG. 7 illustrates a prior art FinFET semiconductor device.Three-dimensional FETs (FinFET) have been designed to facilitateincreased device density. FinFETs use a polysilicon conductor routedover vertical sides and top of a fin (i.e. FinFET body), to facilitatescaling of CMOS dimensions, while maintaining an acceptable performance.In particular, the use of the FinFET structure suppresses Short ChannelEffects (SCE), provides for lower leakage, and provides for more idealswitching behavior. In addition, the use of the FinFET structureincreases polysilicon shape area, which allows the FinFET to have bettercurrent control, without increasing the polysilicon shape length of thedevice. As such, the FinFET is able to have the current control of alarger two-dimensional FET without requiring the device space of the twodimensional FET. FIG. 7 illustrates a source 75 and drain 76 which areformed on an oxide 72. A polysilicon shape 78 is forms the gate for theFinFET. A thin oxide 77 separates the silicon fin comprising source 75and drain 76.

FIG. 8 is a top view illustration of a prior art FinFET design comprisedof polysilicon shape 84, having polysilicon shape 84 covering bothvertical sides and top of FinFET 80. A via 81 is used to form anelectrical coupling between a source 82 and a metal layer 83.

FIG. 9 is functionally similar to FIG. 8. Bridging vertices 92 couplesource 91 to polysilicon conductor 93. Polysilicon shape 94 is the gateelectrode of FinFET 90. FIGS. 8 and 9 are not drawn to scale, however,savings in metal wiring space, are saved when electrical couplingsbetween FinFETs and other microelectronic devices are implemented usingbridging vertices.

The use of bridging vertices can be extended beyond the application ofFETs. As described in the background, electrical measurements must betaken between the polysilicon shape and the silicon area duringmanufacture. If the amount of measured error exceeds a predeterminedamount specified by a process designer, steps must be taken to correctthe problem or discard the faulty product. Two common measures ofmanufacturing precision are bias and alignment. Bias refers to thevariation in the size of the silicon area or polysilicon shape relativeto a predetermined specification. Alignment refers to the orientation ofthe polysilicon shape relative to the silicon area. In the followingdescription, bias and alignment measurements are first explainedseparately to clearly illustrate each of the two measures and then themeasures are described in conjunction with one another.

A measurement apparatus 100A is shown in FIG. 10A, which performs themeasuring function. A silicon area 101A is formed with a plurality ofpolysilicon shapes 102A, 102B (enclosed in dashed lines) formed on twoor more sides of silicon area 101A. A first polysilicon shape 113A isformed near silicon area 101A, and a second polysilicon shape 114A isformed directly facing first polysilicon shape 113A creating apolysilicon shape pair 103A (enclosed by dotted line). First polysiliconshape 113A has bridging vertex 115A and second polysilicon area 114A hasa bridging vertex 116A. A distance 110 exists between bridging vertex115A and bridging vertex 116A. Distance 110 may remain constant or varydepending on the design of the apparatus for other instances of apolysilicon shape pair. Each polysilicon shape pair 103 is uniquelyoriented relative to silicon area 101A and all polysilicon shapes areprocessed by the same mask, therefore, have the same alignment relativeto silicon areas. As previously described, if for example bridgingvertex 115A is overlapping silicon area 101A, an electrical bridge willoccur at bridging vertex 115A. Therefore, an electrical test can beapplied to measure the orientation of each polysilicon shape pair 103 bydetermining if an electrical bridge exists. An electrical bridge can bedetermined by measuring some electrical quantity. The electricalquantity could be resistance, voltage, current, or any other electricalquantity. The electrical measurements could be obtained through anynumber of means including but not limited to pad cages, probing, or apass gate multiplexor.

By equally spacing each polysilicon shape pair according to distance 110with unique orientations relative to silicon area 101A, the presence orabsence of electrical bridges can be used to determine alignment ofpolysilicon shapes to silicon area 101A. In an exemplary embodiment asshown in FIG. 10A, a properly aligned polysilicon shape pair 103C ischaracterized by the occurrence of an electrical bridge on a bridgingvertex 115C and an electrical bridge on a bridging vertex 116C. If anelectrical bridge is observed on only one polysilicon shape of apolysilicon shape pair 103C, then the polysilicon shape pair 103C is notproperly aligned with silicon area 101A. When a plurality of polysiliconshape pairs exist, each polysilicon shape pair can be systematicallytested to determine if an electrical bridge exists. According to FIG.10A for example, a simple resistance measurement could be made at eachof the polysilicon shapes and a threshold resistance of 10K ohms couldbe chosen. In this case, less than 10K ohms resistance would signify abridge occurs and greater than or equal to 10K ohms would signify anelectrical bridge does not occurs. Ten electrical tests would be run;one test for each polysilicon shape. To quantify results, a 1 wouldrepresent an electrical bridge and a 0 would imply no electrical bridgeexists. The test results of first plurality of polysilicon shapes 102Awould be represented by 11100 when the test begins with the leftmostpolysilicon shape and ends with the rightmost polysilicon shape. Asimilar test could be applied to second plurality of polysilicon shapes102B and test results would produce 00111. Analysis of the results wouldreveal that polysilicon pair 103C is properly aligned as indicated byelectrical bridges occurring on both bridging vertices of thepolysilicon pair. While this example determines proper alignment throughthe detection of electrical bridges, detecting the absence of electricalbridges may also be used in a similar manner.

In addition to measuring the alignment of a polysilicon shape relativeto a silicon area, variation in the size of a silicon area or apolysilicon shape can also be measured utilizing bridging vertices.Those skilled in the art will recognize that variation in the size of asilicon area or polysilicon shape is referred to as bias. In a preferredembodiment, each polysilicon shape pair e.g. 103A, 103B is separated bya constant distance 110.

FIG. 10B illustrates silicon area 101B when it is actually larger thanan expected size, and bias will thus be detected due to the large numberof electrical shorts that will be observed. Solid lines 120A, 120Billustrate the expected edges of the top and bottom sides of the siliconarea 101B. In such a case, more polysilicon shapes 113A, 113B, 114A,114B, etc. will be overlapping silicon area 101B resulting in moreshorts. Similarly, if a silicon area is smaller than expected, implyinga bias is present, fewer or no electrical bridges may be observed. Theabsence of electrical bridges in such a case is the result of a distance110 that is too large for any bridging vertex to overlap silicon area101B. To measure alignment accurately, the total effect of bias on themeasurement must be accounted for. It is possible to compensate forbias, e.g. in FIG. 10B by determining where the transition between opensand electrical shorts occur in two or more pluralities of polysiliconshapes. In FIG. 10B, a first open can be observed on bridging vertex115E of a first plurality of polysilicon shapes 102A and a second opencan be observed on bridging vertex 116A of a second plurality ofpolysilicon shapes 102B. Determining a horizontal distance 130 between afirst open (at bridging vertex 115E) on the top side of silicon area101B and a second open (at bridging vertex 116A) on the bottom side ofsilicon area 101B, properly aligned polysilicon shape pair 103C can belocated by averaging horizontal distance 130. Generally, a properlyaligned polysilicon shape pair is located by determining the horizontaldistance existing between the two opens nearest the properly alignedpolysilicon shape pair wherein the first open must be located on a firstside of a silicon area and the second open must be located on the sideopposite the first side of a silicon area. Similarly, to compensate fora silicon area exhibiting bias where the silicon area is smaller thanexpected, the same procedure may be used, but instead measuring shortsin place of opens to determine the horizontal distance.

The combined effect of bias and alignment on measurement results can nowbe explained in greater detail. FIG. 11 is a table containing variouscombinations of bias and alignment. For this table, assume 1=short (i.e.polysilicon shape is electrically bridged to a silicon area) and 0=open(i.e. polysilicon shape is not electrically bridged to a silicon area).Further assume a grid is superimposed over the polysilicon shape andsilicon area and each graduation in the grid has a value of one gridpoint. It should be noted that the grid superimposed in FIG. 12 is notdrawn to scale and is shown only to indicate that a grid is used whendetermining the positions of polysilicon shapes relative to a siliconarea. The positioning of each polysilicon shape ranges from +10 gridpoints relative to the silicon area to −10 grid points relative to thesilicon area. A polysilicon shape positioned 10 grid points to the rightwould be considered +10 grid points, and similarly a polysilicon shapepositioned 10 grid points to the left relative to the silicon area wouldbe considered −10 grid points. Each polysilicon shape in a pair ofpolysilicon shapes (e.g. a left polysilicon shape and a rightpolysilicon shape) has a specific orientation based on the grid. Whenthe polysilicon shape pair is aligned appropriately with the siliconarea and no bias exists, the polysilicon shape is defined to be properlyaligned. Therefore, each silicon shape may assume 21 different positionswhen a position 0 is included. FIG. 12 illustrates polysilicon shapes atdifferent positions relative to the silicon area. The open/shortrelationship between the position of the silicon shape and thepolysilicon area are illustrated in the number sequences found in FIG.11.

FIG. 12A will be used to illustrate the relationship between rightpolysilicon shapes 12A, silicon area 12B, and left polysilicon shapes12C when measuring bias and alignment using measuring apparatus 12 whereno bias or misalignment exists. Case 1 of FIG. 11 is illustrated in FIG.12A, wherein an aligned polysilicon shape pair 12D is perfectly alignedand silicon area 12B has no bias. Column B of FIG. 11 illustrates eachopen/short value for left polysilicon shapes 12C. Similarly, Column C ofFIG. 11 illustrates each open/short value for right polysilicon shapes12C. In Case 1 where no bias exists, correct alignment occurs at anoffset of zero grid points for both the right polysilicon shape and theleft polysilicon shape of aligned polysilicon shape pair 12D. It ispossible that a measuring apparatus may measure misalignment when nobias is present as described in Case 2 and illustrated in FIG. 12B. Nobias can be assumed because 12 shorts are observed implying no more andno less silicon area is present than expected. If bias was present andmore silicon area was present, an accompanying increase in shorts (1's)should be observed resulting from more polysilicon shapes in contactwith the silicon area. In Case 2, the measuring apparatus indicatesmisalignment because the short/open test results of the left side (shownin FIG. 11 Column B) reveal fewer shorts and the right side reveals asurplus of shorts. It can be inferred from the surplus of four shorts inColumn C and shortage of four shorts in Column B that misalignment ofthe polysilicon shape pairs is four grid points to the left.

Case 3 of FIG. 11 (illustrated in FIG. 12C) is an embodiment displayingboth misalignment and bias. Bias can be inferred by the presence of 16shorts indicating the silicon area has increased in size by 4 gridpoints. Examining the numerical open/short representation forpolysilicon shapes on the left side, it could be inferred that thepolysilicon shape pairs are shifted to right five grid points; however,the numerical open/short sequence in Column C indicates the right sideis shifted to the right by one grid point. To resolve the alignmentdiscrepancy of each side, the surplus of shorts is averaged between thetwo sides and the correct measurement of misalignment is three gridpoints to the right. Case 4 of FIG. 11 illustrates an unusable productor faulty test. The random occurrences of shorts and opens reveal faultyfabrication, damage to the device, or some other event rendering thedevice useless. Bias and misalignment cannot be measured based on suchresults.

The following teaches an embodiment of a measurement method beginning atstart step 100 utilizing bridging vertices and shown in FIG. 13A. In afirst step 101 of a method of measuring alignment of a plurality ofpolysilicon shapes to a silicon area, a plurality of polysilicon shapepairs are formed, and each polysilicon shape in the plurality ofpolysilicon shapes has a bridging vertex. Furthermore, each bridgingvertex has a unique orientation relative to the silicon area. In asecond step 102, it is determined for each polysilicon shape if anelectrical bridge exists between the polysilicon shape and the siliconarea. The measurement tests are repeated as indicated by 103 until allpolysilicon shape pairs have been tested. The method ends at step 104.

Step 102 is further comprised of two additional substeps as indicated inFIG. 13B. A start step 105 begins the submethod. In a first step 106, across-reference is created between electrical connections andnon-electrical connections of each polysilicon shape and the siliconarea versus alignment and bias. In a second step 107, an electricalquantity is measured between each polysilicon shape and the siliconarea, which may be resistance, voltage, current, or any other electricalproperty. Alignment and bias are determined using the cross-referenceand the electrical quantity. The method ends at step 108.

FIG. 14 is a method beginning at step 200 for forming an electricalcoupling between a polysilicon shape and a silicon area on asemiconductor chip. In a step 201, a polysilicon shape having a bridgingvertex is formed. Electrical couplings between silicon areas andpolysilicon shapes may only be created when a bridging vertex is createdover the silicon area. The bridging vertex is formed when a portion ofthe polysilicon shape has an angle less than or equal to a criticalangle. The critical angle ensures that the spacer width will besufficiently small enough near the bridging vertex to create anelectrical bridge between the polysilicon shape and the silicon area. Ina second step 202, a spacer is formed on vertical sides of thepolysilicon shape. The spacer serves as an insulating layer between thepolysilicon shape and the silicon area when a suicide is applied in asubsequent step. Wherever a spacer is present, electrical couplings willnot be formed between the silicon area and the polysilicon shape. In athird step 203, silicide is created on the polysilicon shape and thesilicon area. Where spacers are present, no electrical couplings mayoccur, but electrical couplings will be created between the polysiliconshape and the silicon area at the bridging vertex where the spacer widthis sufficiently small and silicide has been applied. Step 204 ends themethod.

1. A method of measuring a structural characteristic of a plurality ofpolysilicon shapes to a silicon area comprising the steps of: formingeach particular polysilicon shape of the plurality of polysilicon shapesto have a bridging vertex, each bridging vertex having a uniqueorientation relative to the silicon area; and determining for eachparticular polysilicon shape of a plurality of polysilicon shapes if anelectrical bridge exists between the silicon area and each particularpolysilicon shape; and wherein a bridging vertex is a portion of aparticular polysilicon shape on a semiconductor chip, the portion havingan angle, as seen from a top view, acute enough to prevent a sidewallspacer being formed on a vertical surface of the particular polysiliconshape at the bridging vertex during a step of processing thesemiconductor chip having the plurality of polysilicon shapes, includingthe particular polysilicon shape, and the silicon area, thereby allowingsilicide to form on the vertical surface of the particular polysiliconshape at the bridging vertex in a silicide step performed duringprocessing of the semiconductor chip.
 2. The method of claim 1 whereinthe structural characteristic is bias.
 3. The method of claim 1 whereinthe structural characteristic is alignment.
 4. The method of claim 1wherein determining if an electrical bridge exists between the siliconarea and each bridging vertex of the plurality of polysilicon shapesfurther comprises creating a cross reference between electricalconnections and non-electrical connections of each polysilicon shape andthe silicon area versus alignment and bias.
 5. The method of claim 1wherein determining if an electrical bridge exists between the siliconarea and each polysilicon shape of the plurality of polysilicon shapesfurther comprises measuring an electrical quantity between eachpolysilicon shape and the silicon area and determining alignment andbias using a cross-reference and the electrical quantity.
 6. The methodof claim 5 wherein the electrical quantity is selected from the groupconsisting of resistance, current, and voltage.